The Princeton sailwing, developed and researched at Forrestal Research Center in Princeton, N.J., is an aircraft wing of extreme simplicity which consists of a large-diameter round front spar (usually an aluminum tube), a taut flexible rope or cable as the rear spar, and cloth covering both sides. There are no ribs. This principle permits the construction of lightweight wings of high aerodynamic efficiency, with lift/drag ratios as high as 22. It has been suggested to employ these wings for light airplanes, but so far the Princeton sailwing has not yet been widely used because of the severe shortcoming of inherent flutter-instability as explained in the following: If the air stream during flight should strike the Princeton sailwing accidentally from above, not from below as usual, which can occur in a "negative G" maneuver or in a wind gust, the airfoil of the wing can snap into an inverted camber condition where the upper side is concave and the lower side convex. This inverted airfoil produces radical changes in the lift conditions, and dangerous aircraft instability will result.
A general article on the Princeton sailwing, written by Mr. T. Sweeney, can be found in Popular Science, Oct. 1972. In the present invention, this flutter problem is solved, and in addition, the sailwing is made variable in flight, to allow short take-off and landing (STOL) performance, and easy steerability.